Abstract
Betatrophin, also known as ANGPTL8, is secreted by liver and adipose tissue and plays an important role in glucose and lipid metabolism, but the mechanisms behind this remain unclear. Betatrophin is highly activated by active triiodothyronine (T3), a key player in metabolic control, which in turn is activated by bile acids (BA) via the BA-G-protein-coupled receptor TGR5-cAMP-deiodinase (D2), mediating the conversion of prohormone thyroxine to T3. We here measured betatrophin by ELISA and also applied GWAS and targeted metabolomic profiling in 233 serum samples of coronary angiographied patients. We found a correlation between betatrophin and BMI (r=0.142, p<0.001), fasting glucose (r=0.133, p=0.002), insulin (r=0.221, p<0.001), triglycerides (r=0.233, p<0.001), HDL (-0.122, p=0.004), and oxLDL (r=0.247, p<0.001). GWAs also found a genome wide-association between betatrophin and genomic variants in sterol transporter genes ABCG5/G8 and ABCA1. In the metabolomic assay we identified BA as the top metabolites to be associated with betatrophin concentration in serum (CDCA, r=0.234, p<0.001; GDCA, r=0.247, p<0.001; GCA, r=0.269, p<0.001; GCDCA, r=0.268, p<0.001; GLCA, r=0.211, p=0.002; TDCA, r=0.184, p=0.006). In conclusion, this study for the first time describes the association between betatrophin and BA. As (i) T3 is activated by BA via the BA-TGR5-cAMP-D2 signalling pathway and (ii) T3 is a strong activator of betatrophin, the link between betatrophin concentration and BA suggests that, at least in part, the impact of BA on energy homeostasis and metabolic control may be mediated via betatrophin. Moreover, TGR5 receptors have also been identified on pancreatic islet α- and β-cells and are stimulating insulin secretion in β-cells and able to restore β-cell mass and function under hyperglycemic conditions. Altogether, this may elucidate the impact of betatrophin on lipid and glucose metabolism. Disclosure A. Leiherer: None. A. Muendlein: None. K. Geiger: None. C.H. Saely: None. E. Brandtner: None. J. Ebner: None. B. Larcher: None. A. Mader: None. P. Fraunberger: None. H. Drexel: None.
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